Financial Derivative Instruments - Carrying Amount of Fair Value Hedges (Details) - USD ($)		Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Deferred Gain (Loss) on Discontinuation of Interest Rate Fair Value Hedge		$ 19,000,000	$ 20,000,000
Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Amount of Hedged Item		500,000,000	791,000,000
Designated as Hedging Instrument | Short-term Debt
Derivative [Line Items]
Derivative, Amount of Hedged Item		500,000,000	0
Designated as Hedging Instrument | Long-term Debt
Derivative [Line Items]
Derivative, Amount of Hedged Item		0	791,000,000
Cumulative fair value adjustment | Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Amount of Hedged Item	[1]	19,000,000	11,000,000
Cumulative fair value adjustment | Designated as Hedging Instrument | Short-term Debt
Derivative [Line Items]
Derivative, Amount of Hedged Item	[1]	0	0
Cumulative fair value adjustment | Designated as Hedging Instrument | Long-term Debt
Derivative [Line Items]
Derivative, Amount of Hedged Item	[1]	$ 19,000,000	$ 11,000,000

[1] At December 31, 2019 and 2018, these amounts include the cumulative amount of fair value hedging adjustments remaining for which hedge accounting has been discontinued of $19 million and $20 million, respectively.